A wide variety of electrically heatable hoses for use in motor vehicles are known. The medium flowing between two connection points in these hoses is heated by these hoses.
A heatable hose having at least one electrical heating conductor which serves to heat a medium flowing in the hose is known, for example, from DE 102 01 920 A1, wherein the heating conductor extends over at least part of the length of the hose and is composed of a metal core and a sheath.
The heating conductor is usually embedded in a layer of the hose. In a multi-layer hose, the heating conductor can also be arranged between two layers. The ends of the heating conductor are exposed in order to be able to connect them to a voltage source which is required for operating the heating conductor. The exposed ends of the heating conductor are usually arranged at one end of the hose. However, it is also possible for an exposed end of the heating conductor to be arranged at each end of the hose.
The exposed ends of the heating conductor are provided with an electrical connection (plug) and are then connected to a voltage source. Since the voltage source is usually not arranged directly at the hose, the exposed ends of the heating conductor have to have a predefined length in order to form a connection to the voltage source via the plug.
The heatable hose line preferably has two helical heating conductors which are supplied with power at one end and are short-circuited at the other end. This ensures that the line is heated.
EP 1 329 660 B1 discloses a flexible multi-layer heatable hose having at least one reinforcement layer and an elastomeric outer layer as well as an electrical heating conductor which is used for heating a medium flowing in the hose. The heating conductor extends over at least part of the length of the hose and is composed of a metal core and a sheath, wherein the heating conductor is embedded outside the outer stratum of the reinforcement layer but under or within the elastomeric outer layer. In order to permit simple and reliable electrical contact to be made between the heating conductor and a voltage source, the elastomeric outer layer is less strong than the heating conductor and is dimensioned such that the heating conductor can be exposed by means of a radially outwardly acting force by cutting through the original or weakened elastomeric outer layer, but without damaging its metal core and its sheath, and can be connected directly to an electrical connection. The heating conductor preferably runs beneath or within the elastomeric outer layer in a helical manner at least over part of the length of the hose.
The described technology of the heatable hoses has been proven to be useful when transporting liquid media between two connection points or connection nipples of motor vehicle assemblies, for example storage tank, injection unit, pump et cetera. However, in particular applications, it has been found that the liquid medium can freeze in the hose connection nipples of the connecting blocks which are usually in the form of standardized plug connections, in particular quick-action plug connectors, and are arranged at the ends of the hose.
This risk of freezing occurs particularly in exhaust-gas after treatment systems for reducing nitrogen oxide emissions from an internal combustion engine. In this case, nitrogen oxide is converted into atmospheric nitrogen and water vapor with the aid of selective catalytic reduction technology (SCR). The reducing agent used is an aqueous urea solution which is carried along in a separate storage container. The aqueous urea solution is fed out of the storage container by means of a delivery module or a pump and is supplied to a metering module, from which the urea solution is injected in a metered manner into the exhaust-gas flow upstream of the catalytic converter. Excess reducing agent is conducted from the delivery module back into the storage container via a return line.
Hose lines for conveying the reducing agent are provided between the storage container, the delivery module and the metering module. These hose lines have to be connected to said assemblies in order to establish the fluid connection.
For the hose connections to the assemblies, it is possible to insert the quick-action plug connectors, which are standardized in the automobile industry, at the hose ends, the receptacle parts of these hose ends being mounted on the assemblies ex-factory. The quick-action plug connectors (quick connectors) have the advantage of rapid mounting of the hose and a wide variety of embodiments of the quick-action plug connectors are known. They are most frequently designed as a “male part” on the assemblies and as a “female part” on the hose ends, the latter having a connection nipple for the hose end, onto which the end of the hose which is to be connected is pushed and fastened such that it is media-tight.
The hose lines between the reservoir container and the exhaust gas line have to be capable of being heated, since below −11° C. there is a risk of the aqueous urea solution freezing. It is known to avert the risk of freezing by using the known, electrically heatable hoses. Although these electrically heatable hoses have been proven to be useful, in extreme applications the plug connectors are the weak point of the exhaust-gas treatment systems in respect of the risk of freezing. There is still a risk of freezing in the plug connections themselves.
In order to provide an apparatus which protects against freezing of the aqueous urea solution even in the connections of the hose lines to the assemblies which are to be connected, it has already been proposed to use connecting blocks which can be heated by cooling water for the hose connections. These connecting blocks are designed in such a way that the cooling water, of which the temperature can be controlled, is flushed through them. As a result, both the hoses and the plug connectors can be thawed.
The use of special quick-action plug connectors (quick connectors) which have a separate electrical heating element (for example a heatable ceramic component) is also known. This has the disadvantage of being a very expensive and complex solution which also requires an additional electrical connection (plug).
In order to measure the concentration of urea in the solution during the injection process, a sensor is inserted into the pipe or hose line via a junction piece (T piece, Y piece), wherein the hose line has to be disconnected. The region of the junction piece is also subject to the risk of freezing. This region of the hose line should therefore be electrically heated too. However, no heatable designs are known for these junction pieces at present because two hose ends meet at a disconnection interface.